QUES:
Who is it in the following sentence?

The infection spread throughout the building because it was airborne.

ANS:
The infection


QUES:
Who is he in the following sentence?

John bought a beer for Bill because he likes cool guys.

ANS:
John


QUES:
Who is they in the following sentence?

The zombies chased the survivors because they were tasty.

ANS:

the survivors